Maximize Cluster Power

Choose some disjoint triples of servers; each group's power is the median of its three values. Any server may go unused, and building no group at all is also allowed; maximize the sum of the groups' medians.

输入格式

The first line contains n; the second line contains the powers. The original text had no numeric bounds; this site uses 1≤n≤200000, −10^9≤power≤10^9; this site includes negative powers, and groups with negative gain need not be built.

输出格式

Output a single integer, the answer.

样例 1

输入：

6
1 2 3 4 5 6

输出：

8

样例 2

输入：

3
-3 -2 -1

输出：

0

样例 3

输入：

4
8 8 1 1

输出：

8

样例说明

The answers are 8, 0 and 8. With negative values, building no group gives 0 instead of being forced to build one.